Field of the Invention
The present invention relates to fluid miniscule volume dispensers and more particularly to a air displacement micropipette dispenser tip for dispensing volumes of fluid whereby very accurate dispensations of less than 5 microliters can be achieved.
Description of the Prior Art
There have been many types of fluid fluid volume dispenser tips employed in the past and many have been designed for the purpose of attempting to transfere accurately measured small amounts of liquid. Some are positive displacement micropipettes utilizing plungers to squeeze out the desired amount of fluid. The problem with those devices is that they are expensive to manufacture and as a result must be reuseable, and when reused, offer the risk of contamination because the fluid transferred is in direct contact with the plunger. Air displacement micropipettes on the other hand contain the fluid to be transferred wholly in the tip with an air volume interfacing between the plunger and the fluid.
One of the primary problems encountered with dispensing small amounts of fluid occur as a result of the physical phenomena of capillary action and surface tension. Alone or in combination these two phenomena (if they can be differentiated) cause the fluid being forced out of the dispenser tip to enlarge in size until it is of a weight to overcome the cohesive force of the surface tension of the liquid to separate from the dispenser. This droplet size is dependant upon many factors and is often larger than the amount of liquid desired to be dispensed. Various attempts have been made to design dispensing tips which cause small drops to separate off the end of the tip of the dispenser but largely without a great deal of success. The reason this is important is that in dispensing a volume of fluid, a droplet usually remains on the tip of the dispenser. The present invention solves the problem and causes very small droplets to be formed.